The devices used in wireless networks are increasingly lightweight and small so as to respond to the requirements of users. Hence, the antennas designed for such terminals must have a reduced size while offering high performances.
However, although significant miniaturization is observed in the field of electronics, the laws of physics impose a minimum size for an antenna in order for it to function correctly in a given frequency band. Hence, for printed antennas, the dimensions are generally in the order of the wavelength at the central operating frequency.
Several techniques have been proposed for reducing the size of the antennas while retaining their radio-electric performances relating to yield, frequency bandwidth and radiation pattern.
Hence, in the French patent application no. 01 08235 filed on 22 Jun. 2001 in the name of THOMSON Licensing S.A., a description is made of an annular slot type planar antenna in which the slot has been shaped to extend the perimeter of this slot. This enables either the substrate dimensions to be reduced for a given frequency, or, at constant dimensions, to modify the operating frequency.